1. Technical Field
The present invention relates to the development of latent images using charged toner particles, and more particularly to a development method and apparatus involving a toner pre-charging capability.
2. Background Art
In electrostatographic copiers and printers that produce or reproduce copies of images, it is well known to use charged toner particles, from a quantity of such particles held at a development station, to develop latent electrostatic images on an image-bearing member. As is also well known, the quantity of such toner particles being held at each development station can be contained at a desired concentration in a multiple-component developer material. As images are developed by using up such toner particles, their quantity so held at the development station is gradually depleted through such use, and therefore must be replenished periodically in order to maintain their desired concentration.
Typically, as disclosed for example in U.S. Pat. No. 5,079,590, issued Jan. 7, 1992 to DeCecca; U.S. Pat. No. 4,615,606, issued Oct. 7, 1986 to Nishikawa; and U.S. Pat. No. 4,924,270, issued May 8, 1990 to Sako et al, replenishment of toner particles as such is carried out from a supply of fresh uncharged toner particles held in a supply hopper. The particles are fed from the supply hopper to the development station where they are then charged before being used for image development. Typically, the charging of the toner particles in the development station is accomplished by rubbing them with oppositely-charging carrier particles either directly on the surface of a transport roller which transports them to an image development area, or alternatively in a sump portion of the development station. In the sump portion, they can be moved, mixed and triboelectrically charged along with oppositely-charging carrier particles for a necessary interval of time in order to achieve a desired charge level on the toner particles before they are transported to an image development area.
Unfortunately, however, the quantity of charged toner particles required from one time to another for image development can vary significantly depending on the density and extent of toner particle laydown of images being developed. As such, the rate at which fresh uncharged toner particles, as above, are replenished or added to the development station therefore also varies. Therefore, when images which require large amounts of charged toner particles are being developed, large amounts of fresh uncharged toner particles must be added to the development station.
In modern high speed reproduction apparatus which include such a development station, there is an increased risk that poorly charged toner particles will be transported to the image development area of the station due to a lack of sufficient time at the high reproduction speed to necessarily move, mix and triboelectrically charge the freshly added uncharged toner particles, along with the depleted developer material in the development station, to the desired level. Such a risk can result in development defects such as wide lines and background contamination. Additionally, such a risk can result in undesirable toner particle dusting out of the development station, and hence contamination elsewhere within a host reproduction apparatus.